1. Field of the Invention
The present invention relates to an agent for susceptive diseases which contains as an effective ingredient a novel polypeptide that induces the interferon-.gamma. (hereinafter abbreviated as "IFN-.gamma.") production by immunocompetent cells.
2. Description of the Prior Art
It is known that IFN-.gamma. is a protein which has antiviral-, antioncotic- and immunoregulatory-activities, and which is produced by immunocompetent cells stimulated with antigens or mitogens. Because of these biological activities, IFN-.gamma. was expected to be used as an antitumor agent since its discovery, and is studied energetically in clinical trials as a therapeutic agent for malignant tumors in general, including brain tumors. Commercially available IFN-.gamma. preparations are roughly classified into two groups, i.e. a group of natural IFN-.gamma.s produced by immunocompetent cells and a group of recombinant IFN-.gamma.s produced by transformants, obtained by introducing into microorganisms of the species Escherichia coli DNAs which encode the natural IFN-.gamma.s. In the above clinical trials, one of these two groups of IFN-.gamma.s is administered to patients as an "exogenous IFN-.gamma.".
Among these IFN-.gamma.s, natural IFN-.gamma.s are usually produced by culturing established immunocompetent cells in nutrient culture media supplemented with IFN-.gamma. inducers to form IFN-.gamma.s, and purifying the formed IFN-.gamma.s. It is known that the type of IFN-.gamma. inducers greatly influences the IFN-.gamma. yield, as well as on the ease of IFN-.gamma. purification and the safety of the final IFN-.gamma. containing products. Generally, mitogens such as concanavalin A (Con A), Lens culinaris, Phytolacca americana, endotoxin and lipopolysaccharide can be used as an IFN-.gamma. inducer. However, these mitogens have the problems of molecular varieties and quality changes depending on their origins and purification methods, as well as the difficulties in obtaining preparations having a constant IFN-.gamma. inducibility in a desired amount. In addition, most of these mitogens might induce unfavorable side effects when administered to living bodies, and some of them may even cause toxicity, so that it is substantially difficult to induce the IFN-.gamma. production by directly administering IFN-.gamma. inducers to living bodies.
Recently, some pharmaceuticals, which contain as an effective ingredient cytokines such as interferon-.alpha., interferon-.beta., TNF-.alpha., TNF-.beta., interleukin 2, and interleukin 12, as well as IFN-.gamma., were developed or are being explored for actual use. These pharmaceuticals can be used as an antitumor agent, antiviral agent, antiseptic or immunoregulatory agent and, if necessary, they can be used together with other medicaments.
Unlike chemically synthesized pharmaceuticals, the aforesaid pharmaceuticals have as the greatest feature the characteristic that they can be administered to patients for a relatively-long period of time without inducing serious side effects, but they also have the demerits that their therapeutic effects are generally relatively-low, and they could not substantially remit and cure diseases when used alone, with the results varying depending on the types of diseases and symptoms to be treated. Therefore, these pharmaceuticals are now used as a supplemental agent for chemically synthesized agents in the treatment of serious diseases such as malignant tumors or used to prolong the patients' life.